1. Step-Input Tracer Tests
Working with a reactor at a bench scale imposes certain restrictions. Among them, the limited flow rate range due to reactor and tubing dimensions may be the most important one. It is virtually impossible to fully introduce a significant volume of tracer by an instantaneous pulse in the reactor’s inlet. Consequently, performing an input step tracer experiment on such unit becomes challenging and the results are inaccurate. This was confirmed while running pulse step experiments for a previous research. Therefore, step input tracer tests were performed instead, using sodium chloride as a tracer and conductivity as the traced parameter.
To perform the step input tracer test in the laboratory, low conductivity water or fluid A was initially fed to the reactor at a constant flow rate until it was completely filled and steady state was achieved. Then, at a time designated as
t
0=0
, the influent to the reactor was rapidly switched to high conductivity water or fluid B and simultaneously, the first sample of the effluent stream taken. After this first sample, taken att
0, the effluent stream was sampled every 5 seconds and its conductivity measured until the conductivities of the effluent and fluid B became equal.The output data from this test was recorded as time vs. conductivity for a given reactor configuration, fluids A and B rate of flow and conductivity.
Step-input experiments were performed for different reactor configurations and flow rates. Tests were run with the electrode’s openings oriented both horizontally and vertically and, in each case, with a flow rate through the reactor of 1.0 and 0.5 L min-1.
The results of this first set of experiments with horizontal electrode’s slots are presented graphically in figures 15 and 16. Figure 15 shows the tracer response for an 8-cell reactor with the slots in horizontal position and a flow rate of 0.5 L min-1 through it. Figure 16 shows the results for a similar experiment but with a flow rate of 1.0 l min-1 through the reactor. Detailed results are shown in the appendix, tables 4 and 5.
41 Figure 15. Tracer response curve for an 8-cell reactor with horizontal slots and Q=0.5 L min-1
Figure 16. Tracer response curve for an 8-cell reactor with horizontal slots and Q=1.0 L min-1
Similarly, another set of experiments was carried out using the same 8-cell configuration but rotating the electrodes by 90 degrees so that their slots were now oriented vertically. The tracer response was recorded for the 8-cell reactor with vertical slots and flow rate of 0.5 L min-1 and 1.0 L min-1 and plotted in figures 17 and 18, respectively. Results are summarized in the appendix, tables 6 and 7.
Figure 17. Tracer response curve for an 8-cell reactor with vertical slots and Q=0.5 L min-1
Figure 18. Tracer response curve for an 8-cell reactor with vertical slots and Q=1.0 L min-1
The following group of experiments consisted in performing the same step input test but varying the number of cells from one to eight for a fixed flow rate. For these, the electrode’s slots were kept vertically oriented. Figure 19 presents an example of the results obtained from the tracer tests corresponding to a 1-cell through a 4-cell reactor with a flow rate of 1 L min-1 through it. Note that the conductivity of fluid A and B was not the same for all the experiments in this series. Further data manipulation is necessary to be able to compare and analyze these results.
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Figure 19. Example of step input tracer test results for reactor with vertical slots and flow rate of 1.0 L min-1
Complete results are presented in the appendix, tables 4 through 7, along with those obtained for a flow rate of 0.5 L min-1.
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2. Electrocoagulation Experiments
A series of electrocoagulation experiments were performed running a constant flow rate of 1 L min-1 of the synthetic emulsion described in the previous section through the reactor. Aluminum electrodes with their openings oriented vertically were used as both cathode and anode (the reasons for this configuration are detailed later). For each experiment, 8 L of SE were passes through the reactor, the effluent was collected after 5 min of operation in a clear 2-L capacity container and the final sample was drawn through a valve located at the bottom of the container after a 10-min separation time. Hexane extractable materials or HEM were measured in each sample using method 10056.
As with the step input tracer test, the reactor was fractioned in its individual electrochemical cells so that the effluent could be characterized at different lengths from the reactor’s inlet point. Thus, electrocoagulation experiments were run in a 1-cell through an 8-cell reactor. The data obtained from these experiments was recorded as HEM in the effluent vs. number of cells for a given SE composition, flow rate current intensity and applied potential.
Table 1. Electrocoagulation experiments results
Table 1 and figure 20 show the results obtained in electrocoagulation experiments running 1 L min-1 of a constant composition influent stream (SE), aluminum electrodes with vertical slots and average applied potential of 33 volts.
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Figure 20. Electrocoagulation experiments shown as HEM vs. number of electrochemical cells.
Processing of this data is presented in the following section and will allow determining the kinetic constant
k'
for EC under similar operational conditions.0 100 200 300 400 500 600 0 1 2 3 4 5 6 7 8 HEM concentration, mg/l Number of Cells Data points
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